抄録
The latitudinal variation of phytoplankton community structures was estimated from
phytoplankton pigment analysis in western Pacific Ocean (140°E-175°E, 30°N-25°S). Surface
water was collected during the overseas educational cruise of Tokai University from February 15
to March 31, 2002. 8 pigments including chlorophyll a (Chla) were identified and quantified by
reversed-phase HPLC. Chla concentration and the pigments composition changed distinctly
across 25°N to 30°N where temperature fronts were found. On the north side of the front,
Chla concentration was more than 0.2ug/L.The maximumvalue was 0.58ug/L in the late March,
which was explainedas a spring bloom.The fucoxanthin and 19'-hexanoyloxyfucoxanthin, which
stand for diatoms and prymnesiophyte, respectively, varied proportional to Chla concentration.
On the other hand, zeaxanthin contained in cyanobacteriaand prochlorophyte dominated in the
southern part of the front where Chla concentration was low (＜0.1ug/L). Zea : Chla ratio showed
the highest value, 0.237 ± 0.139, in this area. Summarizing these results, we show that diatoms
and prymnesiophyte increase inshore, whereas picophytoplankton including cyanobacteria and
prochlorophytedominates more than 80% in oligotrophic waters of offshore.
